Abstract
Following a large outbreak of foodborne gastrointestinal (GI) disease, a multiplex PCR approach was used retrospectively to investigate faecal specimens from 88 of the 413 reported cases. Gene targets from a range of bacterial GI pathogens were detected, including Salmonella species, Shigella species and Shiga toxin-producing Escherichia coli, with the majority (75%) of faecal specimens being PCR positive for aggR associated with the Enteroaggregative E. coli (EAEC) group. The 20 isolates of EAEC recovered from the outbreak specimens exhibited a range of serotypes, the most frequent being O104:H4 and O131:H27. None of the EAEC isolates had the Shiga toxin (stx) genes. Multilocus sequence typing and single nucleotide polymorphism analysis of the core genome confirmed the diverse phylogeny of the strains. The analysis also revealed a close phylogenetic relationship between the EAEC O104:H4 strains in this outbreak and the strain of E. coli O104:H4 associated with a large outbreak of haemolytic ureamic syndrome in Germany in 2011. Further analysis of the EAEC plasmids, encoding the key enteroaggregative virulence genes, showed diversity with respect to FIB/FII type, gene content and genomic architecture. Known EAEC virulence genes, such as aggR, aat and aap, were present in all but one of the strains. A variety of fimbrial genes were observed, including genes encoding all five known fimbrial types, AAF/1 to AAF/V. The AAI operon was present in its entirety in 15 of the EAEC strains, absent in three and present, but incomplete, in two isolates. EAEC is known to be a diverse pathotype and this study demonstrates that a high level of diversity in strains recovered from cases associated with a single outbreak. Although the EAEC in this study did not carry the stx genes, this outbreak provides further evidence of the pathogenic potential of the EAEC O104:H4 serotype.
Highlights
The Enteroaggregative Escherichia coli (EAEC) group is a large, diverse group of diarrhoeagenic E. coli originally defined by their adherence to HEp-2 cells in a stacked brick formation [1]
Virulence gene content associated with EAEC is highly variable between different strains, as illustrated in studies aimed at genotyping EAEC from a variety of clinical sources, healthy control groups and outbreaks [6,7,8,9]
The faecal specimens had been stored for over 10 weeks at 4uC, an attempt was made to isolate the pathogens detected by the multiplex PCR by testing individual colonies for the stx, ipaH and aggR target genes, associated with Shiga toxin-producing Escherichia coli (STEC), Shigella species and EAEC respectively
Summary
The Enteroaggregative Escherichia coli (EAEC) group is a large, diverse group of diarrhoeagenic E. coli originally defined by their adherence to HEp-2 cells in a stacked brick formation [1]. Virulence gene content associated with EAEC is highly variable between different strains, as illustrated in studies aimed at genotyping EAEC from a variety of clinical sources, healthy control groups and outbreaks [6,7,8,9]. In these studies, strains show inconsistent presence and concordance of EAEC virulence genes by PCR in specimens from symptomatic and asymptomatic cases. These data suggest that the full genetic component of this phenotype is not yet fully understood and, most of these genes are found on the aggregative virulence plasmid, their inheritability is complex
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